The invention relates to a device for measuring capacitively the level of a fluid in a tank or container.
In particular the invention relates to a capacitive level gauge which is adapted to be used, for example, in storage tanks (for example on ships or on land), in depots, road tankers, retail stations, etc.
Level gauges based upon the capacitance measurement principle are generally known and operate as follows:
The level gauge consists of two means, for example, isolated metal tubes, placed vertically in the fluid in the tank or container, the two means forming a capacitance. The fluid fills the space between the two means and serves as a dielectric. The dielectric between the two means influences the capacitance value of the gauge. The influence of a determined dielectric on a capacitance value is known to those skilled in the art and will not be explained in detail. Since the dielectric above the level in the tank or container may be a gas and the dielectric below the level may be a liquid, it will be clear to those skilled in the art that from a capacitance-measurement the level of this liquid in the tank can be determined.
It is already known to use a sectionalized level gauge comprising a plurality of sections or segments, means for measuring the values of the segment-capacitance and means for deriving information concerning the level in the tank from the measured capacitance-values. However, such sectionalized level gauges require tight tolerances of the segments or sections when accurate measurements are required. However, obtaining the tight tolerances during construction and assembly is costly and time-consuming.
It is therefore an object of the present invention to provide a simplified and cheap sectionalized level gauge, in particular for use in retail stations, the transmission of the sections not being dependent on the section-tolerances.
It is another object of the invention to provide a sectionalized level gauge which can operate over a large range of temperatures and is suitable for operation in many liquids including crude oil and chemicals.